Ground rod and method of making the same



July 9, 1940. STAPLES 2,207,134

GROUND ROD AND METHOD OF MAKING THE SAME Filed NOV. 30, 1938 INVENTOR #0 4c: ,4; Jmar:

ATTORNEY Patented July 9, 1940 UNITED STATES PATENT OFFICE GROUND ROD AND METHOD OF MAKING THE SAME Application November 30, 1938, Serial No. 243,274

r: 2 Claims.

This invention relates to the science of earthing, more particularly to the grounding electrodes commonly known as ground rods and has for its object to produce a ground rod of economical '5 construction, one that can be readily transported and easily handled without damage mechanically and be inserted in the ground without the use of special driving heads or rods.

It has long been known that copper is the most desirable material for ground rods because of its high electrical conductivity and excellent corrosive' resistance, but it is necessary to use a diameter of rod larger than that ordinarily required to carry the current in order to obtain sufficient surface in contact with the earth and to give proper mechanical strength. This over size increases the cost materially.

To overcome this high cost, thin wall copper tubing has been used provided with a pointed end, and driven into the ground by inserting in the tubular portion a dowel or driving rod provided with a driving head. The force of the blow of the hammer on the driving head is transmitted to the pointed end, thus relieving the strain on the tube. This is not thoroughly satisfactory because the thin unsupported wall of copper is fragile and can only be used in relatively soft soil, and for the further reason that when the force of the blow is transmitted to the point through a bouncing dowel inserted in the tube, vibrations are set up within the structure that retards its progress in the earth requiring much more foot pounds of energy.

I have discovered that when I reinforce a thin wall tube by a core of compressed wood or other similar fibrous materiahso that the assembly approaches a complete composite structure it has all the characteristics of a unitary column. With this construction I provide a means of hardening the fibrous structure and thus place a tension in the wall of the tubing producing high frictional grip between the two members of the composite body resulting in greater columnar strength than with the two members in merely laminated relation.

By compresing the wood core within the copper tube to a point of minimum absorption, expansion due to moisture absorption is practically eliminated. By using a hexagonal tube, I provide for any slight expansion that might occur within the tube thus ensuring a long life to the rod.

A ground rod constructed as above described can be driven into the ground with 35 to 40% less foot pounds of energy than is required with a ground rod of similar size and point, but with a wooden dowel inserted in the tube without any compressing of the wood.

A further object of this invention is to produce a grounding rod of sufficient surface and 5 electrical area compatible with lightness and strength. To achieve this end a thin wall tube may be used of any cross section desired as will be readily understood.

The foregoing and other features of my invention will now be described in connection with the accompanying drawing forming part of this specification in which I have represented my ground rod in its preferred form after which I shall point out more particularly in the claims those features which I believe to be new and patentable.

In the drawing:

Figure l is a side elevation of my ground rod in its preferred form having a conductor clamp on one end.

Fiigure 2 is a side elevation of same at right angles to that shown in Figure 1, the conductor clamp not shown.

Figure 3 is a section along the line 33, Figure 2, looking towards the right.

Figure 4 is a section along the line 4-4, Figure 1, looking towards the left.

Figure 5 shows a section of a modified form which I may employ.

In the carrying out of my invention I use a wooden or other fibrous material core I0 which is inserted within a thin wall metal copper tube II. I prefer to use a hexagon shaped tube for the reason that it has a greater area of copper in its exposed surface than a round tube of the same unit cross sectional area and further for the reason it provides for any expansion of the filler that may take place due to absorption of water or other causes. This tube and filler is then drawn down to a reduced diameter, by any well known means so that the O. D. of the finished rod after drawing is smaller than the diameter of the filler rod. This compressing of the wood produces a filler that will not readily absorb moisture and consequently will not swell and burst the copper tube. It also keeps the copper tube under tension, increasing the frictional grip betwen the two members forming a composite body.

On one end I secure a pointed conical member l2 provided with a shank l3 adapted to screw, into the wood as shown in Figure 1 or be driven into a hole in the wood provided for the purpose as shown in Figure 2. It will be observed that the 55 base M of the conical portion of the member I2 is the same diameter as the long diameter of the hexagonal rod. With this combination, it will be observed that the base l4 extends beyond the sides of a hexagon rod so that the friction between the hexagon sides and the ground in which the ground rod is driven is materially reduced thereby requiring less number of blows to drive the rod, home.

The angle of the conical point is substantially equal to the angle of flow or angle of repose of the material in which the ground rod is to be inserted.

On the end of my rod opposite the point I2, I provide a clamp I8 of any well known type, adapted to firmly contact an electrical conductor I9 to the ground rod ll. The clamp is secured to the ground red by any well known means such as a. set screw 2| as shown.

It will be readily understood that I may use any cross sectional shape of thin wall tubing, without affecting the novel features of my invention and that various sizes may be used depending on conditions of service.

As an example: To produce a O. D. rod, I use a wooden rod of at least diameter with a copper tube having 0. D. and I. D. When this combination is drawn to O. D. the wood filler core is compressed from 30% to 40%. This hardens the fibrous structure of the wood and produces high frictional grip between the two members and reduces to a minimum the wa ter absorption of the filler.

With the member I2 inserted so that the conical base I4 is; tight up against the end of the core I I, every ounce of energy of the blow on the end 20 is transmitted direct through the composite column structure to the pointed tip, thereby facilitating its insertion in the ground with 50% less foot pounds of energy in some cases, than now used with any ground rod on the market.

A tubular ground rod O. D., with a pointed end driven in the ground by the use of a driving rod or dowel inserted within the tube takes an average of 460 blows of a 31# hammer falling 12" and striking the movable inserted wooden rod within the tube. Whereas when the compressed core is within the tube as set forth in this application to form a unitary column, it only requires an average of 285 blows.

These tests were made at Bayway, New Jersey,

in homogeneous New Jersey clay where the energy required could be compared.

I am aware that copper clad steel, and/or other metal, core rods have been used before and I disclaim any use of metal on metal ground rods. There is a distinct disadvantage of using a copper on metal rod because of the battery effect set up when the two metals are in the presence of moisture which shortly disintegrates one of the metals, thereby destroying the effectiveness of the ground. In my rod with copper on wood no such effect is observed.

In the commercial manufacture of these rods the Wooden drOWBl may be slid into a thin wall tube and drawn through dies in any well known manner so that the core is compressed to a point of minimum absorption.

I wish it distinctly understood that my ground rod and method of making it as described and illustrated is in the form and manner in which I desire to construct it and that changes or variations may be made as may be convenient or desirable without departing from the salient features of my invention and I therefore intend the following claims to cover such modifications as naturally fall within the lines of invention.

I claim:

3.. A ground rod comprising a thin wall tube of conducting material having a core of radially compressed wood of density of minimum absorption, said core held by the tube to its reduced diameter under compression whereby the maximum columnar strength of the complete rod is obtained, a conically pointed end provided with a shank tightly fitting into the core and held by the compressed fibrous material and abutting the core and tube.

2. A ground rod comprising a thin Wall tube of hexagonal cross section having a reinforcing within the tube of radially compressed wood to form a composite columnar structure, a driving tip having a conical point and a shank adapted to be fitted into a recess in the wood and be held under compression of thewood, the base of the conical point having the same diameter as the long diameter of the tube section whereby the ground friction of the hexagonal sides is materially reduced when driving the rod into the ground.

HORACE A. STAPLES. 

